This invention relates to a gear synchronizer shift arrangement for motor vehicle transmissions and more particularly to such an arrangement which may be incorporated into a vehicle transfer case for a four wheel drive vehicle.
It is known to use a transmission type strut synchronizer clutch arrangement to provide on the go two-wheel to four-wheel drive mode shifting for a transfer case drive assembly. An example of one such arrangement shown and described in S.A.E. Technical Paper Series No. 800002, entitled "Internal Transfer Case Controls for Four Wheel Drive Vehicles" by G. E. Huffaker, dated Feb. 25, 1980, discloses a part-time transfer case gear synchronizer clutch. The transfer case provides a two-wheel drive operating state wherein the main shaft directly drives a tubular extension which, in turn, drives the rear axle output shaft through a gear connection in the inter-axle differential. A fork mechanism shifts a synchronizer clutch sleeve into engagement with external splines of a silent chain carrier placing the transfer case in its four-wheel drive mode delivering power via a drive chain to the vehicle front drive shaft. In such a synchronizer shifting operation there may be a slight manual or mechanical induced time delay or slippage in the shifting sequence resulting in lagging travel of the shift fork apparatus. In the event of such slippage the synchronizer sleeve internal splines are unable to advance smoothly to initially engage the chain carrier splines without some undesirable shifting resistance and/or gear noise.